A solid-state imaging device is roughly divided into a complementary metal oxide semiconductor (CMOS) image sensor and a charge coupled device (CCD) image sensor.
The shutter system of the CMOS image sensor is divided into two systems, namely, a mechanical shutter system and an electronic shutter system. The CMOS image sensor mounted on a mobile device such as a cellular phone equipped with a camera having been remarkably popularized in recent years mainly employs an electronic shutter system in order to downsize the device.
The electronic shutter system is classified into a rolling shutter system and a global shutter system depending on the exposure system. The rolling shutter system sequentially reads out signals line by line. This system of reading out signals line by line in order involves an occurrence of a “konnyaku phenomenon (in Japanese) meaning rolling shutter distortion” due to a reading time difference occurring between lines within one frame. In contrast, the global shutter system performs simultaneous exposure on an entire frame in the reading, and thus would not cause distortion in an image even when a fast moving object is photographed.
In order to implement simultaneity of storage in individual pixels, the CMOS image sensor of the global shutter system includes a charge holding element (capacitor) for each of the pixels and simultaneously transfers the charges generated in the photoelectric conversion element to the charge holding element to be held in the element, thereby enabling global shutter photographing. However, occurrence of light leak into the charge holding element during the charge holding might cause optical noise and this might lead to degradation of image quality.
Patent Documents 1 and 2 disclose technologies for implementing the global shutter system in a back-illuminated CMOS image sensor and suppressing the above-described optical noise. The solid-state imaging element disclosed in each of these documents includes a light shielding metal that covers the charge holding element from the light incident side, thereby providing a structure in which the light shielding metal extends along a region between the charge holding element and a photoelectric conversion unit.